The present invention generally relates to the use of dissolved gases within liquids, such as the separation of contaminants from contaminated liquid. More particularly, the present invention resides in a process of introducing a large volume of gas into a given liquid.
The introduction of gas, such as oxygen, into a liquid is necessary for many processes. For example, when removing contaminants from a contaminated liquid source using flotation methods, gas is dissolved or otherwise entrained into the liquid so that flocculation and separation can occur to remove the contaminants. In other processes, a gas, such as CO2, is introduced into the liquid to alter the pH of the liquid. In yet other processes, oxygen is dissolved into the liquid to support biodegradation.
The hydrocyclone has been used as a separator of particles with different specific gravities for years. In an effort to reduce bubble residence time, a variation of the general hydrocyclone, the air-sparged hydrocyclone described in U.S. Pat. No. 4,279,743 utilizes a combination of centrifugal force and air sparging to remove particles from a fluid stream. The stream is fed under pressure into a cylindrical chamber having an inlet configured to direct the fluid stream into a generally spiral path along a porous wall. The angular momentum of the fluid generates a radially directed centrifugal force related to the fluid velocity and the radius of the circular path. The porous wall is contained within a gas plenum having gas pressurized to permeate the porous wall and overcome the opposing centrifugal force acting on the fluid.
In operation, the unit receives and discharges the rapidly circulating solution while the air permeates through the porous wall. Air bubbles that emit from the wall are sheared into the fluid stream by the rapidly moving fluid flow. The invention claims that micro-bubbles formed from the shearing action combine with the particles or gases in the solution and float them toward the center of the cylinder as froth in a vortex. The centrally located froth vortex is then captured and exited through a vortex finder disposed at the upper end of the cylinder while the remaining solution exits the bottom of the cylinder.
One variation in the general ASH construction, as described in U.S. Pat. Nos. 4,838,434 and 4,997,549, includes employing a froth pedestal at the bottom of the cylinder to assist directing the froth vortex through the vortex finder. Another ASH modification includes replacing the vortex finder and froth pedestal with a fixed splitter disposed at the bottom of the cylinder and having a cylindrical knife-edge. The edge is positioned to split the helically flowing solution into components dependent upon the specific gravity of the components.
However, it has been found that traditional hydrocyclones, including air-sparged hydrocyclones, essentially stratify the various components of the contaminated fluid according to specific gravity. The inventors have discovered in working with ASH Systems, that the helically flowing solution only splits into stratified components if the specific gravity is less than 0.5 or greater than 1.7 of the fluids specific gravity, and the particle size is larger than 10 microns. Without these conditions, the liquid cyclone or hydrocyclone becomes a mixer. Properly designed, this mixer can continuously position or xe2x80x9cmixxe2x80x9d the fluids particles (from water molecules to suspended solids) into the boundary layer or energy interface of the swirling film of liquid and the gas.
Accordingly, there is a continuing need for a process which dissolves a great deal of gas into a target liquid. The present invention fulfills this need and provides other related advantages.
The present invention resides in a process for dissolving a gas into a liquid. The process of the present invention enables the dissolution of gas into the liquid at greater concentrations and saturations than previous methods with a mechanically simple design which is relatively inexpensive to produce and maintain.
The process of the present invention entails first pressurizing the liquid to a predetermined level. The pressurized liquid is directed into a hydrocyclone to form a vortex stream having an evacuated central area. The hydrocyclone is selected to have an inlet aperture size and configuration corresponding to the liquid pressure, and a barrel diameter and length optimized for liquid particle movement through the liquid vortex stream.
Pressurized gas is then injected into the evacuated area for absorption into the liquid vortex stream. Due to the fact that the hydrocyclone inlet, barrel diameter and barrel length have been optimized for liquid particle movement, a large degree of gas is adsorbed into the liquid.
The liquid is then directed from the hydrocyclone into a diffusion column, where the liquid flows upwardly into a pressure chamber. The pressure chamber includes an upper gas region and a lower liquid region. The non-adsorbed gas is collected in the upper gas region.
The gas within the upper gas region, in a particularly preferred embodiment, is directed from the pressure chamber back into the evacuated area of the vortex stream so as to recycle the non-dissolved gas. The level of the gas within the pressure chamber is sensed, and pressurized gas is added into the pressure chamber when the gas level of the pressure chamber falls below a predetermined level.
The liquid having dissolved gas therein is then passed from the pressure chamber and typically through a cavitation plate. The liquid is then used in the desired process, such as biodegradation, contaminant removal by flocculation and flotation, etc.
Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.